1. Field of the Invention
The present invention relates to a TV receiver which receives both an analog broadcasting signal and a digital broadcasting signal and then processes the received analog and digital broadcasting signals. The present invention relates, more particularly, to a TV receiver having an analog/digital dual tuner and control unit for automatically controlling the radio frequency (RF) gain of the dual tuner.
2. Description of the Related Art
A general automatic gain control (AGC) circuit automatically controls the gain of an amplifier so that the level of an output signal is constant although the level of an input signal varies. The AGC circuit used in a TV receiver automatically controls an RF gain of the RF amplifier employed in a tuner and the intermediate frequency (IF) gain of an IF amplifier connected to an output end of the tuner, and thus maintains the level of a restored video signal to be constant although the level of a received broadcasting signal varies.
Meanwhile, an advanced TV receiver can receive and signal-process both an analog broadcasting signal in an analog broadcasting mode and a digital broadcasting signal in a digital broadcasting mode, and restores the received broadcasting signal into an original video signal to then be displayed on a screen.
Referring to FIG. 1, a conventional advanced TV receiver having an analog tuner and a digital tuner, where the RF gain of each is individually controlled, will be described.
The TV receiver of FIG. 1 includes a block for receiving and signal-processing a digital broadcasting signal to be restored into a baseband digital video signal, and a block for receiving and signal-processing an analog broadcasting signal to be restored into an analog composite video signal.
A digital tuner 10A receives a digital broadcasting signal and then selects a channel corresponding to a channel select control signal output from a controller 18. The tuner amplifies an RF signal of the selected channel according to a digital automatic gain control signal AGCd feedback from a digital automatic gain controller 14A, and converts the amplified RF signal into an IF signal. A digital IF processor 12A amplifies and detects the IF signal from the digital tuner 10A and restores the resultant signal into a baseband digital video signal. The digital automatic gain controller 14A generates a digital automatic gain control signal AGCd for lowering an amplification factor of a high-frequency amplifier (not shown) employed in the digital tuner 10A if the output level of the digital IF processor 12A is higher than a predetermined value. The controller 14A also generates a digital automatic gain control signal AGCd for increasing an amplification factor of the high-frequency amplifier (not shown) if the output level of the digital IF processor 12A is lower than a predetermined value. The generated digital automatic gain control signal is supplied to the digital tuner 10A.
Meanwhile, an analog tuner 10B receives a analog broadcasting signal, selects a channel corresponding to a channel select control signal output from the controller 18. It then amplifies an RF signal of the selected channel according to an analog automatic gain control signal AGGa feedback from an analog automatic gain controller 14B, and converts the amplified RF signal into an IF signal. An analog IF processor 12B amplifies and detects the IF signal from the analog tuner 10B and restores the resultant signal into an analog composite video signal. The analog automatic gain controller 14B generates an analog is automatic gain control signal AGCa for lowering an amplification factor of a high-frequency amplifier (not shown) employed in the analog tuner 10B if the output level of the analog IF processor 12B is higher than a predetermined value. Alternatively, the controller 14B generates an analog automatic gain control signal AGCa for increasing an amplification factor of the high-frequency amplifier (not shown) if the output level of the analog IF processor 12B is lower than the predetermined value. The generated analog automatic gain control signal is supplied to the analog tuner 10B.
A signal processor 15 converts a baseband digital video signal supplied from the digital IF processor 12A and an analog composite video signal supplied from the analog IF processor 12B into a luminance signal and a chrominance signal, respectively, and converts the luminance signal and the chrominance signal into a predetermined display format, to then be displayed on a CRT screen 16. Since the above signal processing method is well known to those skilled in the art, the detailed description thereof will be omitted.
The controller 18 applies a channel select control signal for selecting a corresponding channel to the digital tuner 10A if the channel selected by a user is a digital broadcasting mode, and applies a channel select control signal for selecting a corresponding channel to the analog tuner 10B if the channel selected by a user is an analog broadcasting mode. Accordingly, the digital tuner 10A or analog tuner 10B selects a corresponding channel according to the channel select control signal output from the controller 18.
As described above, since the conventional TV receiver shown in FIG. 1 includes the broadcasting signal processing blocks for respective broadcasting modes independently, there is no close operational relationship between the broadcasting signal processing blocks. The structure of the system is complicated and thereby contributes to production costs. Also, since the TV receiver of FIG. 1 controls the tuners 10A and 10B according to the broadcasting modes of the channels to be viewed, respectively, the control method is complicated and inefficient.
To solve the above problems, it is the object of the present invention to provide a TV receiver having a dual tuner capable of receiving and selecting an analog broadcasting signal or a digital broadcasting signal and a controller for automatically controlling the radio frequency (RF) gain of the dual tuner, in which the system is simplified and the structure is well organized.
To accomplish the above object of the present invention, there is provided a TV receiver for receiving and signal-processing an analog broadcasting signal and a digital broadcasting signal, the TV receiver has a dual tuner for selecting the channel of a corresponding broadcasting mode according to an applied channel select control signal, from among the received broadcasting signals. The dual tuner also controls the gain of a radio frequency (RF) signal of the selected channel according to an applied automatic gain control signal, and converts the gain-controlled RF signal into an intermediate frequency (IF) signal. The TV receiver also has a signal distributor for distributing the IF signal output from the dual tuner according to a broadcasting mode. It also includes an analog processor for amplifying and detecting the analog IF signal output from the signal distributor to be restored into an analog composite video signal and generating an analog automatic gain control signal for controlling the RF gain of the dual tuner in response to the level of the restored signal and a digital processor for amplifying and detecting the digital IF signal output from the signal distributor to be restored into a baseband digital video signal and generating a digital automatic gain control signal for controlling the RF gain of the dual tuner in response to the level of the restored signal. The TV receiver has a switching portion for selecting one of the automatic gain control signals, output from the respective processors, according to an applied AGC select signal and supplying the selected automatic gain control signal to the dual tuner. The TV receiver also has a controller for applying the channel select control signal of each broadcasting mode to the dual tuner and applying the AGC select signal of each broadcasting mode to the switching portion, in response to a user request.